1. Field of the Invention
This invention relates to a system for warming blood and other liquids to physiologic temperature before infusion into a patient. The system is characterized by disposable heat exchanging blood warming envelopes with automatic gas bubble venting and to the provision of active warm air insulation of the intravenous line to the patient.
Blood is stored at approximately 4 degrees C. prior to transfusion and should be warmed to physiologic temperature of about 35 to 40 degrees C. for transfusion. Infusion of cold fluids at high flow rates can cause cardiac arrhythmia, cardiac arrest and death. Even at low flow rates it is desirable to warm intravenous liquids for delivery to the patient, especially if the patient is an infant or child.
In the intravenous administration of blood products and other intravenous liquids, it is necessary that the liquid being administered to the patient be free of entrained air or other gas bubbles to prevent venous gas embolism and its potentially fatal consequences. The present system is designed to deliver warmed liquids from very low flow rates to high flow rates of 500 ml/min. or more. At high flow rates significant volumes of gas bubbles are generated during the warming process. These must be removed before administration of the liquid to the patient.
2. The Prior Art
My prior U.S. Pat. No. 5,013,889 is directed to an electric blood warmer utilizing heating by vapor condensation. The disclosure of that patent is incorporated herein by references.
One commercially available blood warmer which can maintain physiologic temperature to the patient connection is that designated "Hotline" from Level 1 Technologies of Rockland, Mass. This unit, however, can provide flow rates of only 50 ml/min. Level 1 System 250 is a high flow rate blood warmer but utilizes patient intravenous flow lines exposed to room air and at low flow rates delivers liquid to the patient connection at temperatures substantially below physiologic temperature. In that system a hydrophobic film gas vent and filter in the patient flow line is utilized. To prevent air from entering the patient line through the hydrophobic gas vent in the event of sub-atmospheric pressure in the line, a separate check valve element must be incorporated. One object of the present invention is to provide a simplified and economical automatic gas bubble vent incorporated into the plastic heat exchanging envelope, thus eliminating the separate check valve.
George et al U.S. Pat. No. 4,392,858 issued Jul. 12, 1983 discloses a wound drainage device optionally including a gas or air vent covered by a hydrophobic sheet filter.
Sloane et al U.S. Pat. No. 4,294,594 issued Oct. 13, 1981 discloses a filter assembly for removing particulate material, bacteria and air from an intravenous solution which includes hydrophobic filters.
Geller U.S. Pat. No. 4,534,757 issued Aug. 13, 1985 discloses a device for introducing active ingredients into a liquid flow parenteral administration system which includes a receptacle through which the liquid flows having preferably hydrophobic filters.
Greenblatt U.S. Pat. No. 4,707,587 issued Nov. 17, 1987 discloses a blood warming apparatus using a gaseous heat exchange medium.